Conventionally, water having sterilization ability or ability to oxidize a material is used in places where the hygienic environment is emphasized such as a medical establishment, a food plant, a public bath house, a pool or the like.
Examples of such water which are usually popularly used are ozone water in which ozone (O3) is dissolved and water processed by an ultra violet sterilization lamp.
However, it has been pointed out that a large quantity of ozone leaks into the atmosphere from an ozone generator which generates ozone water thus giving rise to possibility of adversely affecting the environment or the like. Further, there also arise drawbacks such as the spreading of the odor peculiar to ozone or a large quantity of power consumption at the time of generation of ozone and hence, there exists tendency that the use of ozone has been recently limited.
On the other hand, it has been also known that active oxygen species which are generated by exciting a photocatalytic reaction by radiating light to a photocatalytic body possess a function of sterilizing microorganisms or a function of decomposing various organic chemical substances by oxidation in the extreme vicinity of a surface of the photocatalytic body (usually, 40 nm). That is, although being observed only in the extreme vicinity of the photocatalytic body, these active oxygen species having high reactivity such as a super oxide anion radical (O2−) or hydro-oxi radical (OH.) are dissolved in water due to contact with water, and transform cell membranes, functional protein, genes or the like of microorganisms or viruses, thus are capable of stopping the survival function or propagation function of microorganisms or viruses.
Accordingly, for example, as shown in FIG. 17 and FIG. 18, there has been proposed a water treatment device having the following constitution for sterilizing the microorganisms in water. That is, an agitating shaft 54 is arranged at a center portion of a cylindrical tank 53 having a water inlet port 51 and a water outlet port 52. Agitating blades 56 each having a mesh-like photocatalytic body 55 are arranged outwardly in the radial direction around the agitating shaft 54. A blacklight 57 for ultra violet radiation is arranged on an inner wall of the tank at a predetermined position. By rotating the agitating shaft 54, a quantity of ultra violet rays which impinge on the photocatalytic body 55 can be increased (see, patent document 1, for example).
According to this water treatment device, the radiation efficiency of ultra violet rays to the photocatalytic body 55 can be enhanced and agitating blades 56 can agitate water and hence, it is possible to sterilize the microorganisms by bringing the microorganisms into contact with active oxygen species generated on a surface of the photocatalyst whereby organic substances in water may be decomposed.
Further, as one of fields which have conventionally required the sterilization of microorganisms, the cultivation of fish is often mentioned.
In general, edible fish are cultivated by extending a fish net in sea water to form a fish preserve, and fish such as seriola, three line grunt or tiger puffer are fed and grown inside the fish reserve.
Such fish cultivation can efficiently acquire by plan various targeted fish compared to the harvesting of fish naturally swimming in the ocean thus contributing to the stable supply of fish to consumers.
Further, the kinds of fish which can be cultivated have increased recently and, at the same time, fish having quality compatible to the quality of natural fish can be cultivated and hence, the steady development of the cultivation industry is expected from now on.
However, in carrying out the fish cultivation, fish are fed and grown in a relatively small fish preserve and hence, once sick fish suffering from microorganisms or parasites appear in the fish preserve, other fish in the fish preserve are infected by the sick fish thus giving rise to possibility that the number of sick fish or dead fish will increase one after another.
Particularly, in fish cultivation which advertises the efficiency and ease of planning as advantages thereof, the massive spread of sick fish or dead fish due to parasites causes immense damage to the cultivation business leading to confusion in supply of fish to markets.
Fish parasites which bring about such fish sickness can be, in general, classified into two kinds of parasites, that is, ectoparasites represented by Benedemia seriola, Heteraxine heterocerca, and endoparasites represented by lumen endoparasites such as anisakis, organization endoparasites blood vessel trematode such as myxosporidia.
These parasites are further sub-classified depending on the kind of fish and various studies have been made with respect to respective host specificities.
In general, the influence of parasites on the host is mainly attributed to respiration disorder and maintenance management disorder of body fluid attributed to osmotic pressure failure.
With respect to endoparasites such as blood vessel trematode, rather than a drawback caused by the parasite per se, it is necessary to focus on a drawback that the parasite lays eggs and these eggs clog a fine blood vessel of a gill of fish when a large quantity of eggs is discharged into the fine blood vessel thus suffocating fish.
Further, the ectoparasites adhering to fish suck blood from the host at adhering positions and acquire nutrition from the host. The ectoparasites which adhere to epithelium cause an epithelial cell damage thus damaging the fish body parasitized with ectoparasites. Particularly, when the gill is infected with the ectoparasites, this infection causes peeling-off of a respiratory epithelial cell, the inflammation attributed to hyperplasia and a rod-shaped change and these changes are irreversible thus causing the vegetative growth failure attributed to respirational disorder.
Particularly, ectoparasites often adhere to a portion of the fish body where sea water is in contact and hence, there exists high possibility that ectoparasites float per se and eggs thereof in sea water and infect other fish. In this manner, ectoparasites are considered to be one of parasites which cause large damages on the cultivation business.
Accordingly, as a means for preventing or curing sickness attributed to infection of ectoparasites, there has been known a following method (see patent document 2, for example). That is, when ectoparasites are Benedemia seriola, a fresh water bath is particularly effective to protect marine fish. When ectoparasites are Heteraxine heterocerca, porous carriers impregnated with hydrogen peroxide water are scattered in a fish preserve to protect marine fish. Due to the performance of hydrogen peroxide, parasites or microorganisms are emasculated thus preventing and curing sickness attributed to infection of ectoparasites.
According to this method which uses hydrogen peroxide water, it is possible to attenuate possibility that cultivated fish die out due to parasites or microorganisms.
However, the above-mentioned water treatment device which includes the agitating blades requires large agitating blades for enhancing the efficiency of photocatalytic reaction. Accordingly, to produce water containing a sufficient quantity of active oxygen, there exists a drawback that the device per se becomes large-sized. Further, the oxidizing ability continues for an extremely short time, that is, 10−6 second and hence, a reaction phase takes only in an extremely limited and extremely narrow region of the photocatalytic body leading to the acquisition of insufficient sterilization effect.
Further, although the device may be miniaturized by miniaturizing the photocatalytic body, lowering of photocatalytic reaction efficiency is not overcome and hence, the reduction of the device is not realized at present.
Still further, in the large-sized device, to drive the agitating shaft, large electric power sufficient to cope with water resistance is necessary and hence, the device is not desirable also from a viewpoint of energy efficiency.
Further, as a photocatalytic body provided to the agitating blades, a photocatalytic body which applies titania coating to a surface of fiber-like aluminum is exemplified. However, the mere application of titania coating to the surface of fiber-like aluminum exhibits poor photocatalytic reaction and hence, it is difficult to efficiently produce water containing activated oxygen.
Further, in the above-mentioned method which treats the cultivated fish with hydrogen peroxide water (referred to as hydrogen peroxide water bath in general), a strong oxidization power of hydrogen peroxide affects the cultivated fish per se. That is, it is not deniable that this method is directed, rather than to the recovery of fish by reducing parasites adhering to the cultivated fish, to the elimination of sickness-weakened fish with parasites and the revival of only strong fish.
The weakened fish dead due to scattering of hydrogen peroxide reduces a catch quantity of cultivated fish leading to the lowering of cultivation efficiency. It is apparent that if parasites can be eliminated from the fish infected with parasites while assuring the safety of such fish, the catch quantity of cultivated fish can be increased leading to the lowering of distribution prices of fish as well as the assurance of safety of foods.
Further, the effective concentration of hydrogen peroxide to be scattered in sea water is required to exhibit the high concentration up to 200 to 3000 ppm. Although hydrogen peroxide is diluted, in the same manner as a conventional balnea medicata method such as a formalin bath, hydrogen peroxide is directly flown out, scattered and thrown away in the ocean. Hydrogen peroxide also affects other marine organisms besides the cultivated fish. Accordingly, the cultivation of fish using hydrogen peroxide is hardly preferable from a viewpoint of environment, and the influence of hydrogen peroxide on human being is not yet determined.
Still further, to achieve a parasite elimination effect, a large quantity of hydrogen peroxide agent becomes necessary, and a cost necessary for preparation of hydrogen peroxide and man-power necessary for transportation of hydrogen peroxide impose a large burden on staffs in charge of such labors.
In the cultivation business which has such drawbacks, there has been a demand for an apparatus and method for producing photocatalytic reaction water for eliminating parasites which do not use medicines which remain in sea water, which do not damage cultivated fish, and do not influence the environment.
Accordingly, inventors of the present invention have made extensive studies on an apparatus for producing photocatalytic reaction water which can produce water containing sufficient quantity of active oxygen species, can eliminate microorganisms and parasites, can maintain strong oxidation ability, can save power, can be formed small, and is applicable to various devices, and have made the present invention.    [Patent document 1] JP-A-2001-327961    [Patent document 2] JP-A-03-200705